Printing process



1946- E. JAHODA 2,412,889

PRINTING PROCESS Filed Feb. 16, 1945 Molar Pandas s' ms 6 40::

4 INVENTOR. 'W ;M BY

Patented Dec. 17, 1946 PRINTING PROCESS Edward Jahoda, Detroit, Mich'.,"am; to Walter M. Fuchs, Detroit, Mich.

Application February 16, 1945, Serial No. 578,187

This application relates to the art of printing, using the retro-gelatinprinting process.

In that process, an original whose image lines contain a primarychemical, such as potassium dichromate, is caused toengage a moistgelatin coated plate, the coating being sensitized by the inclusiontherein of a secondary chemical, such as ferrous sulphate. The contactof the original image with the ferrogelatin coating causes the engagedportions of the ferrogelatin coating to be chemically aflected orhardened selectively and superficially, that is, only on the surface, toform against the unaflected parts of the ferrogelatin coating, whichremain soft or unhardened, a superficial image whose lines are oxidizedor dulled or hardened. 'I'he hardening which forms the image is merelysuperficial and selective, that is to say, the hardening occurs only atpoints where the markings of the original,

containing the primary chemical, make contact with the gelatin, but issufficient to have a greater affinity for greasy printer's ink than thebackground which, when sufllciently moist, has no such affinity. It isknown that, in printing with a ferrogelatin coated plate so affected byan original image, hereafter known as a printing plate, it is desirableto keep the gelatin coating surface moist, that is, to maintain what istechnically called a water "balance" for such surface.

One way of maintaining such water balance I is to provide a highhumidity for the room. This has obvious disadvantages, but is anaccepted practice.

Another way of maintaining water balance, is to apply water to theprinting surface by spraying or otherwise wetting it directly. This isnot desirable, because it has been discovered that when water is applieddirectly to the printing surface, it has a tendency to spread unevenly,and also to emulslfy with.the ink.

A third way is to load the gelatin with a hygroscopic material such asglycerine. This is also undesirable since glycerine coated materials aredificult to handle and store.

In commercial practice, particularly where a gelatin coating is spreadon a supporting table in a humid room, it is common practice to scrapeoil or otherwise remove the gelatin coating fairly frequently, let ussay, after a few hours of use,

and to spread a new and fresh coating. This has obvious disadvantagesbut it has been accepted as part of the practice in this art.

Now, I have contemplated using, as the gelatin printing plate, a papersheet coated with gelatin.

1 Claim. (01. 101-1493) 2 However, I observed that if the gelatincoating were to be used at ordinary room temperatures, which in warmweather may exceed 975 F., good reproduction results would be diillcultto obtain. Consequently, in warm weather, it would be necessary tomaintain low room temperatures and this would be costly and diilicultand annoying. Therefore, I contemplated loading the gelatin with a bodyhardener or tanning agent, such as formaldehyde, or chrome alum, butthis also would be unsatisfactory. Ii little tanning agentwere used, thegelatin coating would not become sufficiently tanned except after beingaged" or "cured by storing the coated paper for a long time, to attainsufllcient tanning. Thereafter the coated paper would be usable,provided not too long a time elapsed before use: otherwise the coatingwould become excessively water repellant. It is observed thatexcessively tanned coatings would not function well inthe process,primarily because, of the lack of capacity to absorb suflicient waterfor good reproduction. On the other hand, if much tanning ag nt wereused, the coating would tan quickly, but this would require immediateuse of the paper, and this, would not always be feasible. In addition,the use of tanning agents would reduce the quality and ease ofreproduction.

In this application, I disclose a solution to the problem of maintainingwater balance, now encountered in the art of printing by thei'errogelatin process. Briefly, it may be character.- ized as using apaper printing plate and wetting it from the back, the moisture passingthrough the plate to the printing surface. This way of maintaining waterbalance is extremely effective and desirable. Using this way, it isunnecessary to control the humidity of the room in which the printing isbeing done, nor is it necessary to wet the printing surface from thefront, and run the risk of emulsifying the ink.

The invention may be practiced by providing, as the printing plate, athin sheet of water absorbent, wet strength paper, coated with gelatinand laid down on a moist smooth rubbing pad. The paper sheet provides aneconomical, renewable, inexpensive to discard, stable, printing plate,which is not only superior to presently known plates because it may bewetted from the back, but in addition, can be renewed quickly,inexpensively, and very conveniently, after its gelatin coatinghas hadits effectiveness destroyed by the changes whichhave taken place in itduring the printing operation.

The present invention is also directed to the auaase problems of makingthe printing plate, that is,

coated paper to be stored indefinitely, used whenever desired, and usedat ordinary room temperatures even in warm weathen and to the use ofsuch coated paper for reproduction, at ordinary room temperature, evenin warm weather.

Briefly, the coating herein disclosed is substantially untanned, havinglittle or no tanning agent. Kept dry, it may be stored indefinitely.Paper coated with untanned gelatin, may be packaged in cut sheet or rollform, and if protected against moisture, as by being wrapped in waxedpaper, may be stored.

In use, the paper may be wetted from the back. I have discovered,however, that when the wetting pad II is made of a porous stone block,moisture is evaporated, and such evaporation functions to cool thegelatin coating sufficiently to enable untanned coatings to be used atordinary room temperatures with good results.

It seems, therefore, that a solution to all problems is offered by theadoption of back wetting, by the use of a porous stone block as thewetting block or pad, and by the use of untanned-gelatin for thecoating.

For a further understanding of theinvention hereof, reference should behad to the appended drawing which shows a plate ID in the form r of asheet of water absorbent wet strength paper,

coated on its upper surface with untanned gelatin, and disposed upon amoist porous stone block or pad II. A suitable moisture suppl for thepad may be provided, if needed, to maintain the pad ll continuouslymoist.

The printing plate I is a sheet of wet strength saturating paper, coatedon its upper surface with untanned gelatin. It can be manufactured to besold dry, in cut sheets or rolls, and is perfectly stable under ordinarystoring and handling conditions. It is economical, easy to make, andeasy and satisfactory to use.

The printing plate hereof may bev and preferably is free of glycerinsince it is not required to be hygroscopic, for it is not intended thatthe water balance for the gelatin surface be maintained'by absorption ofmoisture from the air, but rather it is intended that the water balancebe maintained by the transfer of moisture from the pad ll, through theprinting plate itself, to the printing surface. Thus the printing platehereof is far less affected by storing and handling conditions thanplates containing glycerine in which water balance is maintained by thehygroscopic action of the glycerine.

The paper functions as a moisture transfer medium, to transfer moisturefrom the source, name- 'ly the pad II, to the gelatin surface, and thusis required to be of a character that retains its strength during themoisture transfer. Forthis purpose, it might well be any well known wetstrength or saturating or absorbent paper. One paper that has been foundsuitable is a paper obtained from the Brown Paper Company, and known asNo. 201 Aqualized Kraft." Saturating tissue, such as is sold by theProcess Manufacturing Company of Chicago, Illinois, has been foundsatisfactory. Vegetable parchment papers have also been foundsatisfactory. A paper known as L99, of Byron Weston Co., Dalton, Mass,has also been foundsatisfactory.

The paper need not have any capacity for stor-.

ing moisture, since only its moisture transfer characteristic is reliedupon to maintain the water balance.

' 4 With gelatin. the usual plasticizers, filler, etc.,

-all well known to the art, may be and preferably should be incorporatedwithin the coating. Howformed with the secondary chemical of thatprocess, ferro sulphate or its equivalent. Instead, the gelatin may beplain, but it will be sensitized or activated, Just before it is engagedby the original, by dampening or moistening it with a farm sulphatesolution. This may be done from the front or the back. Thereafter, themoisture balance for printing is maintained by the transfer of moisturethrough the printing plate from the back, where the printing plate is incontact with the wet pad. While it is contemplated to apply thesensitizing solution from the front, it is, of course, obvious that ifdesirable, it also might be applied from the back, but except insofar asthe sensitizing is a moistening step, this is not particularlyimportant.

The pad H is a porous stone block. One form of block, now being sold byFiltros Incorporated (formerly General Filtration 00., Inc.) of EastRochester, New York, under the trade-mark Filtros, and described by thatcompany, in a bulletin entitled Filtros Plates," copyright 1944, as awhite rigid, porous, mineral substance, composed essentially of silica,and which might be termed as an artificial porous stone has been foundsatisfactory.

It has been found that maintaining the water balance for printing in themanner herein described, by transfer through the printing plate evenlyabsorbed by the gelatin, with no excess,

and without drops of water on the surface, and consequently, there is notendency for the printing ink to spread or emuisify with water.

Further, it has been found that where it is attempted to wet theaffected printing plate from the front, great skill, complicatedapparatus, considerable time, frequent interruption of production, arerequired, and even under the best of operating conditions andperformances, unevenness of distribution of the moisture occurs, withthe result that the ink spreads, or emulsifies, and the unaffected orunhardened or background portions of the gelatin swell unevenly aroundthe chemically aflected or hardened or image portions of the gelatin tocause hills and valleys on that coating, and reproduction is not sosatisfactory. Where there is unevenness of distribution of the moisture,either no swelling of the unhardened gelatin background takes place, orelse the swelling of the unaffected or unhardened gelatin isaccompanied" by a similar swelling of the chemically affected andsuperficially hardened gelatin image. Where the moisture passes throughthe paper, entering from the back, as in the present case, theundesirable conditions and factors are eliminated, and, with lessdifficulty, better reproduction is obtained.

If desired, the paper may be supplied with wetting agents, having atendency to increase the absorption and transfer qualities of the p per.

These agents might be applied to the paper during the manufacture of thepaper, or might be incorporated in the wetting solution.

' Wetting from'the back is of particular value where gelatin coatingsare thin, as for example, where the gelatin is in the form of a thincoating, applied to paper, and stored dry. Withsuch plates, the wetting-and maintaining of water balance is a far more delicate operation, andyet is far more important, than under conditions where thick gelatincoatings, frequently renewed, are used in humidity controlledrooms.

Using a wet porous stone block as the wetting pad is of especialimportance, inasmuch as it functions to cool the paper, thus enablingpapers having untanned gelatin coatings to be used at ordinary roomtemperatures, with good results,

- and thus enabling coated papers to be stored and kept indefinitely, tobe useful for reproduction by the ferrogelatin process. I

Now having described the art of printing herein disclosed, referenceshould be had to the claim which follows:

I claim:

In the art of printing with moisture repelled, greasy printers ink withanon-hygroscopic, initially untanned gelatin surfaced, thin, waterabsorbent, wet strength paper printing plate having a superficialprinting image of hardened gelatin on and surrounded by an unhardenedferrogelatin background, the image having been produced on thebackground by surface contact thereof with an original image containinga primary chemical which reacts superficially with the fer- 'rogelatinbackground to harden the engaged portions thereof to form the selectiveand superficially hardened image, so that there is unhardened gelatinunderlying the image area as well as surrounding it, the step of feedingmoisture to the plate from the back thereof, so that the moisture passesthrough ,the plate to the printing surface thereof, thus maintaining thewater balance therefor, and also maintaining a constant .minimumdifferential of level of the image and non-image areas, by applying thepaper to and in contact with a moist porous stone block which wets andcools the paper.

EDWARD JAHODA.

